“By the Seashore” Performed by Arts on the Horizon. Visit the website for ticket availability. Thursday, Friday, Tuesday and Wednesday at 10:30 a.m. Saturday at 10 and 11:30 a.m. Through July 29. The Lab at Convergence, 1819 N. Quaker Lane, Alexandria. 703-967-0437. artsonthehorizon.org. $6.

Fast Fridays and Slowdown Sundays Features outdoor fitness classes led by instructors from area studios. Friday from noon-1 p.m. Sunday from 9:30-10:30 a.m. Through Aug. 27. John Carlyle Square, 300 John Carlyle St., Alexandria. 703-746-3855. alexandriava.gov. Free; bring a mat and water.

Breast cancer patients with children support group Discuss living with cancer and raising a family, facilitated by a professional counselor and patient navigator. Second Friday from 1-2:30 p.m. Virginia Hospital Center, Cancer Resource Center, 1701 N. George Mason Dr., Arlington. 703-558-5555. Free; registration required.

STEM professionals needed Assist K-12 science teachers as part of the American Association for the Advancement of Science’s STEM Volunteer Program, a partnership with county public schools to bring the real world of STEM into the classroom. Recruiting now for placement during the 2017-2018 school year beginning in September. For more information, please contact Robert Thomas at 301-570-2811 or robert.james.thomas@verizon.net.

Twilight Tattoo: A Military Pageant Features 3rd U.S. Infantry Regiment soldiers and ceremonial units, the Old Guard Fife and Drum Corps, the U.S. Army Drill Team, the U.S. Army Blues, a soloist from the U.S. Army Chorus, and vocalists of the U.S. Army Band Downrange and U.S. Army Voices. 7 p.m. Fort Myer, Summerall Field, Sheridan Avenue, Arlington. 202-685-2888. usarmyband.com. Free.

“The Mark of Cain” For age 13 and older, about a kind of distillation of human history seen through the eyes of Cain, civilization’s first criminal. Mature content. Thursday-Saturday at 8 p.m. and Sunday at 2 p.m. Through Aug. 13, Synetic Theater, 1800 S. Bell St., Arlington. 866-811-4111. synetictheater.org. $35-$60.

Details: Announcements are accepted on a space-available basis from public and nonprofit organizations only and must be received at least 14 days before the Thursday publication date. Include event name, dates, times, exact address, prices and a publishable contact phone number.